Not Applicable.
Not Applicable
(1) Field of the Invention
This invention relates to control systems for increasing the power efficiency and quality control of a pneumatic or gas power system used to power a variety of pneumatically operated processes.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Manufacturing facilities often use compressed air or other gas, for example, nitrogen, as means to power tools, pneumatic transport systems, machines, presses and other production equipment, henceforth designated xe2x80x9ctoolsxe2x80x9d. Compressed air or gas customarily is produced by a compressor or compressors at a central point, stored in a reservoir, and piped to the tools.
The production of compressed air or gas is a major manufacturing expense; it is important to maintain the compressed air or gas system at maximum efficiency in order to minimize energy costs. This invention is used to create a single or multiple-point profile of the gas pressure inputs at a number of points in the compressed air or gas system and within the tools so that the system is operating at maximum efficiency. The profile when compared against the capacitance or storage for the system, process, or tools can be computed against the time register for the computer yielding pressure, rate of flow, rate of change, or both. Such a profile is called a pressure profile, a rate of flow profile, or a rate of change profile. The processes of creation and use of the profile or profiles comparatively is termed SIGNATURE MAPPING, a trademark owned by SDS Management Inc., Mesa, Ariz.
As the plant is operated there is an inevitable movement of the tools from their optimum settings. Contamination of pneumatic circuits with moisture or dirt slowly cause a degradation of the operation. Adjustments in tools change through wear, contamination or unwarranted adjustment by operators. Leaks develop in the pipes, controls and valves. These changes customarily are not recognized until they result in a noticeable decline in productivity or off quality product. At that time the tools are adjusted, the leak is repaired, generally at a substantial cost to productivity. The net effect of such slow and undetected degradation of the pneumatic system is to increase the consumption of power and reduce the productivity of the manufacturing facility.
The present invention continually monitors the pressure readings at the various pressure detectors in the system and compares the readings to the signature map. When an excursion beyond preset limits in the pressure profile is detected at any specific point, the tools are flagged for remedial action, which may be immediate and on-line, or may be stored for analysis by the operator or quality control personnel. SIGNATURE MAPPING is the process of developing the single or multiple point profile and comparing a profile at any specific time with the predetermined profile or map.
Lucas et al. U.S. Pat. No. 4,576,194 discloses a system in which a computer is used to control the supply of air to an output device using the output of the output device to regulate the pressure value leaving the control unit.
Oetiker et al. U.S. Pat. No. 4,597,405 discloses a process for controlling the throughput of pourable or fluid material through a material feed line in a flour mill. The process involves a downstream controller unit and a fluidic pressure drive. The introduction of transient micropressures in the fluidic pressure drive resulted in improved process control.
Brown et al. U.S. Pat. No. 4,665,938 discloses apparatus in which the performance of a current-to-pressure converter which controls the pressure in a system is monitored by a pressure transmitter which feeds-back to a computer information on the pressure actually in the system.
Philbin U.S. Pat. No. 5,190,068 discloses an apparatus in which fluid flow and pressure of fluid passing through a valve is controlled by a computer using information from sensors for pressure and flow upstream and for pressure downstream of the valve and a differential sensor which measures the difference in pressure just above and below the valve.
Wilhelm et al. U.S. Pat. No. 5,319,572 discloses a system for controlling the steam valves in a steam turbine. The system detects malfunctions by sensing temperature, pressure, fluid level, and motor pump current, and either comparing the values to stored previous values or applying diagnostic rules using an artificial intelligence system.
Brown U.S. Pat. No. 5,431,182 discloses a smart valve positioner in which a microprocessor is used to control the valve through a pneumatic actuator in response to sensors of the valve position and temperature.
Castle et al. U.S. Pat. No. 5,493,488 discloses a system for controlling a valve in a pneumatic system.
Fujii et al. U.S. Pat. No. 5,566,709 discloses a system for operating a nuclear power plant in which redundant subsystems such as pumps are normally operated at less than their rated capacity. When one subsystem is out of operation, as for routine maintenance, the other subsystems are increased to their rated capacity, thereby preserving the output of the plant.
Tambini et al. U.S. Pat. No. 5,689,434 discloses a system for monitoring and controlling tools driven by either air or oil. A fluid flow sensor determines fluid flow through the tool, for example, a tool for driving threaded fasteners, and provides information on the torque applied by the tool and the conditions of the tool operation. The information is processed by a computer and displayed in graphic or numerical form.
Foss et al. U.S. Pat. No. 5,632,146, incorporated herein by reference, discloses a system for providing compressed air powered tools and equipment with an adequate supply of compressed air at a satisfactory pressure from a reservoir in which the reservoir is served by two or more compressors which are activated sequentially in response to the air pressure in the reservoir, minimizing the consumption of power by the trim compressor.
None of the prior art disclosures provide a system in which the precise monitoring of pressure and/or rate of flow is used to generate a pressure profile which is subsequently used to detect the slow but correctable degradation of the system or the off quality of the production process, or the precise maintenance requirements of the tools or processes.
This invention, termed SIGNATURE MAPPING, uses one or more pressure transducers which provide an analog output signal calibrated in pressure at pounds per square inch (psig). Such transducers are located at sites of pneumatic or other gas energy discharge, in particular, at or within the tools. Several transducers may be located in one tool, thereby providing extensive information on the operation of the tool. In addition, transducers can be located at various points in the pneumatic power system upstream of the individual tools. The analog signal is converted to a digital signal and transmitted at a speed of 1 MHZ or greater to a computer. The data collected from individual transducers are compared to the signature map. Signature is computed at rates of from one second to 1000th""s of a second.
Signature mapping displays the pressure inputs individually or relative to each other in real time. The profile is always relative to time. The resulting map or signature profile may be pressure, rate of flow, rate of change or both. Rate of flow compares the rate of change of pressure in 10th""s, 100th""s or 1000th""s the capacitance of the system or tool monitored and computes it relative to time in milliseconds. Rate of change is only used relative to the system and is used as an expression of the dynamics of the system. If the power or energy in the using side of the system is equivalent to the supply side, which may include storage, the xe2x80x9crate of changexe2x80x9d is considered neutral or xe2x80x9c0.xe2x80x9d If demand exceeds supply, the rate of change is expressed as negative. If supply exceeds demand, the rate of change is expressed as positive. Negative and positive rates of change are usually expressed quantitatively in mass flow, energy units, or volume.
Data in which the variance from the signature map exceeds a preset tolerance are flagged. The variance may be reduced by on-line remedial actions on the tool or control processes, or the data may be preserved for manual analysis by operators or quality control personnel. Statistical variations in discreet points or sections of the profile or map can be measured to predict maintenance prior to the tool or process exceeding minimum acceptable quality limits.
In addition, the actual signature maps are preserved and may be plotted and printed to serve as a record of the manufacturing process. Such records are useful in quality control analysis, maintenance scheduling, product liability evidence, process improvement planning, and operator and maintenance personnel training.
SIGNATURE MAPPING may be applied to a wide variety of manufacturing processes, including glass bottle, die cast aluminum parts, rubber tire, plastic or polyethylene terephthalate parts or container manufacturing, compressed air and gas system or equipment auditing and analysis equipment, and air jet weaving and spinning.
Examples of tools whose operation may be maximized by this process include high speed pneumatic production transfer and packaging equipment, bag filling equipment, filter presses, dust collectors, bag houses, or reverse pulse filtration equipment, equipment used in porosity or leak testing, and any repeatable pneumatic or gas process including testing protocols.
In discussing the operation of compressed air systems, it is useful to distinguish between compressed air pressure and compressed air flow, rate of flow versus time. Compressed air pressure is expressed in psig. Compressed air flow is expressed in cubic feet per minute, rate of flow (cfm). The readings determined at the various pressure detectors in the system can measure either pressure, rate of flow, rate of change or both. A compressor will produce a certain volume of compressed air in cfm at a certain pressure in psig. A piece of machinery will consume or demand a certain volume or rate of flow of air in cfm at a certain pressure in psig versus time.
In a compressed air system, the compressors will fill the main storage reservoir at a certain pressure in psig. The demand or flow in cfm is a function of the number and consumption rate of the individual pieces of machinery which consume the compressed air, each piece of machinery consuming a certain flow of compressed air in cfm at a certain psig.
In a factory compressed air system the main storage reservoir contains compressed air at a preset pressure such as 110 psig. This pressure is higher than the optimum operating pressure for the machinery, which may be 85 psig. Regulators are used to reduce the pressure of compressed air provided to the machinery from 110 psig to the optimum operating pressure of 85 psig. This arrangement insures that the machinery always receives compressed air at a pressure adequate for the efficient operation of the machinery. In addition, it avoids the wasteful operation of machinery using compressed air at a pressure higher than the optimum pressure for the machinery.
A typical factory compressed air system has two air compressors of 500 hp capacity, a main storage reservoir of 5,000 gal. capacity which contains compressed air at 110 psig, and piping and regulators which provide machinery with compressed air at a regulated minimum pressure of 85 psig. In a typical system, a single base compressor is in operation all of the time the factory is operating, and the trim compressor is activated when the air pressure in the main storage reservoir drops below a preset pressure termed the add point, 100 psig in this example. The trim compressor is inactivated when the air pressure in the main storage reservoir is restored to a preset value, termed the delete point, 110 psig in this example.
In U.S. Pat. No. 5,632,146, incorporated herein by reference, a system termed xe2x80x9cload shapingxe2x80x9d which minimized the repeated operation of the trim compressor with a saving in energy consumption was disclosed. The present invention is effective when used with load shaping or when used in conventional systems without load shaping.
An object of the invention is to provide a pneumatic power system in which the pressure input is detected at each tool while the system is operating at maximum efficiency and recorded by a computer thus creating a pneumatic profile. This pneumatic profile may be pressure, rate of flow, rate of change or both.
Another object of the invention is to provide a pneumatic power system in which a profile of pressures or rates of flow at each tool is recorded by a computer and used to detect disfunction of tools in the system by comparing the pressures or rates of flow with a pneumatic profile or profiles versus time.
Another object of the invention is to provide for the adjustment of pressure at each tool in order to maintain the system at optimum efficiency.
Another object of the invention is to provide a permanent record of the pressure or rate of change or flow profile at each tool for use in quality control and training of operators.
Another object of the invention is to reduce the time required to change production equipment for a run of different product on the same processing equipment.
Another object of the invention is to diagnose and test flow components, such as aerospace parts, assemblies such as combusters or even jet engines.
Another object of the invention is to measure the shape, thickness and porosity of containers during manufacturing.
A final object of the invention is to provide a system and method for insuring the maximum efficiency of a pneumatic power system which is inexpensive, effective, and without harmful effects on the environment.